Method of treating, corrugating and laminating a flexible absorbent sheet material



Oct. 3, 1961 J. H. PICKREN 3,002,873

METHOD OF TREATING, CORRUGATING AND LAMINATING A FLEXIBLE ABSORBENTSHEET MATERIAL Filed Sept. 24, 1957 IN VEJY TOR. Jwzzsfl Piaf/e17,

PM PM ATTORNEYS.

United rates Fatent 7 3,602,873 METHUD OF TREATING, CORRUGATING ANDLAMINATING A FLEXIBLE ABSDRBENT SHEET MATERIAL James H. ltiekren, K0,Box 6466, Jacksonville, Fla, as-

siguor of one-half to Samuel A. Hooker, Martinsvilie,

Filed Sept. 24, 1957, Ser. No. 685,964 2 Claims. ((11. 156-205) Thisinvention relates to a method of treating an absorbent sheet material,and more particularly concerns a method of improving the wet strength offibrous materials such as paper and the like.

This invention further relates to a continuous method of formingfinished articles constructed of fibrous material, such as corrugatedfiberboard or the like, having improved characteristics of wet strengthand water resistance.

It is an object of this invention to provide an improved method ofenhancing the wet strength of sheet materials. Still another object isto provide a method of strengthening fibrous 'sheet'rnaterials suchaspaper and the like. Other objects and advantages of this inventionwill further appear hereinafter.

The drawing illustrates a preferred form of the apparatus for carryingout the method in accordance with this invention, the apparatus beingarranged to produce continuously a corrugated fiberboard pro duct.

In accordance with this invention, a sheet of absorbent material such ascloth, paper, fiberboard or the like is impregnated with steamcontaining a mixture of (1) urea or gelatin and ('2) formaldehyde, andafter the impregnation is complete the product is heated, causing acondensation reaction of the urea or gelatin with the formaldehyde toform a resin in situ which is uniformly dispersed in the sheet.

, Turning now to the specific form of the invention se lected forillustration in the drawings, a roll 10 of flexible absorbent sheetmaterial S is caused to pass over an idler roller ii and then againstthe surface of a corrugator roll 12. A mating corrugator roll 13 isprovided adjacent the periphery of the corrugator roll 12. The sheet Sis continuously subject to a plurality of sprays or jets emanating froma nozzle 14. Several jets 14 are preferably but optionally spaced alongthe edge of the cylinder 12, all such jets being in line so that onlyone is visible in the drawing.

The number 15 designates a tank containing an aqueous mixture of gelatinand formaldehyde. Pipes 16 ex= tend upwardly from the tank 15 and areconnected into the throats of venturis 17. Steam flows at a relativelyhigh velocity through the line 20 and through the venturis 1'7, and thethroats of the venturis accordingly have a reduced pressure causing asuction of the aqueous mixture of gelatin and formaldehyde upwardly fromthe tank 1d. Accordingly, a mixture of gelatin and formaldehyde ofpredetermined proportions is fed into the throat of each venturi l? at arate which is proportional to the rate of flow of steam through theventuri and also to the lineal feet of travel of material through themachine. The steam, mixed with predetermined quantities of gelatin andformaldehyde, then flows upwardly through the pipe 21 to the jets l4,and it is this mixture which is expanded and projected against thesurface of the sheets as the sheet passes around the periphery of thecorrugator roller 12. After corrugation, the sheet 3 passes over anidler roller 22, between rollers 23 and through another steam jetsection 24, wherein additional jets of steam, admixed with urea orgelatin and formaldehyde as heretofore described, are supplied from thepipe 25.

Another sheet S also of flexible absorbent material,

is conducted from a roller 30 over a guide 31 to the steam jet location24, where it is treated (as heretofore described in connection with thesheet S) on both sides with a mix-- provided from a roll 32, whichpasses over rollers 33' through jets contained in the jet portion 24.The sheets- S, S and S are then caused to flow between compressionrollers 34 and between heating elements 35. The heat ing elements applya proper amount of heat to the combined sheets, causing a condensationreaction of the urea and the formaldehyde or the gelatin and theformaldehyde to form a resin in situ which is uniformly dispersed in thesheets.

Because of the fact that the impregnation of the fibrous sheet iscompleted while all of the reactants are in an unreacted condition andin a liquid condition, and because of the fact that the are appliedforcibly in the form of a jet of steam against the surface of theabsorbent fibrous material, an exceptionally good and exceptionallyuniform absorption and penetration of the material takes place. Thisprocess is to be distinguished sharply from processes wherein animpregnation is carried out, using a resin as the impregnating material.In accordance with this invention, the impregiation is brought aboutusing raw materials of a condensation reaction, and after theimpregnation has been completed the condensation reaction is, for thefirst time, started and then completed within the fibrous material."This condensation reaction, involving urea or gelatin I andformaldehyde, is not to be confused with other condensation reactionswhich are known in other arts. It has been found that urea or gelatinand formaldehyde are vastly superior to any other resin formingsubstances when applied to paper, fiberboard or other material, as amixture with steam which is caused to jet against the sufrace of thematerial. Moreover, it has been found that when used on fibrousmaterials such'as paper or fiberboard or the like, the combination ofsteam, urea or gelatin and formaldehyde, followed by heating in a dry.condition, brings about a resinification or a condensation reactionwhich produces an exceedingly stable and exceedingly water resistantresin, such resin being uniformly dispersed among the fibers andpossessing excellent strength qualities over long period of use.

Although the drawings show a specific form of the invention, as appliedto corrugated fiberboard, it should be borne in mind that the processhas application to a single sheet, Whether corrugated or not. Althoughvarious alternate methods may be employed for forming the mixture ofsteam, urea or gelatin, and formaldehyde, the method shown in thedrawings is'of particular advantage since the venturis provide a uniformmixing action which is difiicult to obtain otherwise, and which actionprovides superior results.

The solution contained in the storage tank 15 is preferably a mixture ofurea or gelatin, formaldehyde and water. Where gelatin is employed, thismay be a dilute solution containing, for example, about 6% by weight ofgelatin and about 6% by weight of formaldehyde. The solution may be evenmore dilute, utilizing for example 2% by weight of each such ingredient.However, the dilution is variable within wide limits and may be selectedat the convenience of the operator. Preferably, the total weight ofsolids is in the range of 1 to about 20% by Weight, based on the totalweight of solids plus water, but in any condition the mixture must bereadily llowable. Although it is preferable to maintain the ratio ofgelatin to form-aldehyde at approximately 1-1, this is subject to widevariation since the formaldehyde may be in proportion of one half ofthat of the gelatin, or even less. The

H of the solution is preferably in the range of about 2.2 to 4.5.Phosphoric acid is preferably added in an amount to create a pH withinthis range, and serves as a buffer.

Where urea is combined with formaldehyde, it is preferred to maintain apH of about 4.0 to 6.8, formic acid being added as a bufier in thedilute solution. The solution preferably has a solids content of about1% to by weight, balance water, and for many purposes it is preferred tomaintain, by weight, about 6% to 7% urea plus formaldehyde and 93% to94% water. Ordinarily, only trace quantifies of formic acid produceexcellent results, but more may be added without interfering.

It is preferred in accordance with this method to condition the fibrousmaterial prior to treatment by this process, by treating it with plainsteam. The pressure from the steam in the preliminary process assiststhe impregnation of the paper in the following stages of the process.

It has been noted that the heating of the treated sheet should becarried out in a dry condition. The solution does not provide acompletely workable condensation reaction as long as steam is present.Only when heating is applied in a manner to drive off any remainingwater does the condensation reaction proceed to a proper stage. Thisfactor is highly desirable, since none of the Working parts of theapparatus are clogged up due to polymerization taking place prematurely,as would happen in the case of a urea formaldehyde resin employing acatalyst, for example.

Another advantage of the method in accordance with this invention isthat the mixture of gelatin and formaldehyde or urea and formaldehydeneeds no outside catalyst to cause the condensation reaction to takeplace in the pores of the paper. The dry heat in the drying mechanismcauses the condensation, hence there is no concern with respect to thelife of the solution prior to use. While many other condensationreaction chemicals have a very short pot life due to interaction betweenthem, gelatin and formaldehyde do not react to any appreciable extentuntil they are dry. Although in some cases the boiling of thegelatin-formaldehyde liquid tends to give a small amount of condensationreaction, I have found that by the addition of a small amount ofphosphoric acid (H PO keeping the pH of the solution between about 2.2and 4.5, this condition is avoided.

Referring further to the pot life of a gelatin-type solution, it hasbeen noted that the formaldehyde actually preserves the gelatin andlengthens its pot life, which is sharply distinguishable from otherresin forming chemicals, which tend to react with each other therebyshortening their pot life.

The paper product has a much higher wet strength than conventionalpaper. In fact, strength ratios up to as high as -1 and above have beenobtained as compared to untreated paper. Similar proportion-a1 resultshave been obtained utilizing other forms of fibrous materials.

Another advantage of this invention is that it is unnecessary in manycases to utilize the conventional gluing step which has heretofore beenutilized to adhere the central corrugated portion of a fiberboardproduct to the two fiat outside sheets. The impregnation followed bydrying in accordance with this invention adheres the three sheetstenaciously together, utilizing the condensation product as the adheringmedium.

Paper or fibrous products in accordance with this invention not onlyhave great wet strength, but they breathe and still have a wick actionas did the untreated paper or fibrous product. Water filters through itreadily, notwithstanding the faet that it has been impregnated withresin-forming chemicals which have undergone a condensation reaction.

This invention is applicable not only to fiberboard, paper and the likebut may also be applied to any other flexible absorbent material such ascloth, cardboard, twoply wood, multi-ply wood, etc.

Although this invention hm been described with refere cc to variousspecific embodiments thereof, it will be appreciated that equivalentsmay be substituted for the specific materials, apparatus and methodsteps disclosed herein, and that certain features of the invention maybe utilized independently of the use of other features, all withoutdeparting from the spirit or scope of the invention as defined in theappended claims.

This application is a continuation-in-part of Serial No. 679,797, filedAugust 19, 1957, on my behalf by Samuel Arthur Hooker and now abandoned.

Having thus described my invention, I claim:

1. In a method of treating an elongated piece of fiberboard from aplurality of flexible absorbent sheets of cellulosic material, the stepswhich comprise continuously moving one of said sheets over a generallycylindrical supporting surface having a corrugated formation, providinga liquid treating bath containing an aqueous unreacted mixture of (1) asubstance of the group consisting of urea and gelatin and (2)formaldehyde, said composition being kept at a pH between 2.2 and 4.5when said substance is gelatin and between about 4.0 and 6.8 when saidsubstance is urea, whereby said substance and formaldehyde remainunreacted in the presence of water; flowing a stream of steam past saidbath and constricting the flow of steam to create a venturi effecttherein; withdrawing mixture from said bath and uniformly entrainingsame in said steam flow by means of said venturi effect, the amount ofcomposition withdrawn from said bath and entrained in said steam beingautomatically regulated by the amount of steam passing through saidconstricted flow; directing a jet of steam containing said mixtureagainst said sheet while said sheet is supported by said corrugatedsurface, said steam being under pressure and flowing at a high velocityagainst the surface of said sheet, whereby the sheet is impregnated witha substantially uniform essentially unreacted mixture of said substanceand formaldehyde, continuously adhering substantially flat sheets toopposite sides of the sheet contacted by said steam, substance andformaldehyde, and then heating said sheet to dry same and continuingsaid heating in the dry condition to cause a condensation reaction ofsaid substance and formaldehyde to form a resin in situ uniformlydispersed in said sheet.

2. In a method of treating an elongated cellulosic flexible absorbentsheet material to improve its wet strength, the steps which comprisecontinuously moving said sheet, providing a flow of steam between asource thereof and said sheet material; constricting said flow of steamintermediate said source and said material to create a venturiefiecttherein; providing a liquid treating bath in communication with saidflow of steam adjacent said constricted flow, said both comprising anaqueous composition of (l) a substance selected from t; e groupconsisting of urea and gelatin and (2) formaldehyde, in unreac-ted form,said composition being maintained at a pH between about 2.2 and 4.5 whensaid substance is gelatin and between about 4.0 and 6.8 when saidsubstance is urea, whereby components 1) and (2) thereof remainunreacted in the presence of H 0; withdrawing composition from said bathand uniformly e-ntraining the same with said steam by the action of theventuri effect created in said flow of steam, the amount of compositionwithdrawn from said bath and entrained in said stemn being automaticallyregulated by the amount of steam passing through said constricted flow;directing a jet of the resulting mixture of steam and compositionagainst the surface of said sheet material whereby the material isi1npregnated with a substantially uniform unreacted mixture of saidsubstance and formaldehyde, and then heating said sheet to remove steamand moisture therefrom and continuing said heating in a dry atmosphereto effect condensation reaction between said substance and formaldehydeto form a resin in situ uniformly dispersed in said sheet.

(References on following page) References Cited in the file of thispatent UNITED STATES PATENTS Swift Sept. 26, 1916 Mack Mar. 18, 1930Wrede Nov 20, 1934 Schur Apr. 13, 1937 Bauer et a1 Jan. 26, 1943 Baueret a1 Jan. 26, 1943 6 Newkirk Mar. 30, 1943 Hubbard Nov. 9, 1943 Baueret a1 June 6, 1944 Bryce Aug. 1, 1944 Smidth May 15, 1945 Weisberg et a1Oct. 11, 1949 Harrison et a1 Apr. 11, 1950 Hochberg June 13, 1950TouLmin Sept. 17, 1957

1. IN A METHOD OF TREATING AN ELONGATED PIECE OF FIBERBOARD FROM APLURALITY OF FLEXIBLE ABSORBENT SHEETS OF CELLULOSIC MATERIAL, THE STEPSWHICH COMPRISE CONTINUOUSLY MOVING ONE OF SAID SHEETS OVER A GENERALLYCYLINDRICAL SUPPORTING SURFACE HAVING A CORRUGATED FORMATION, PROVIDINGA LIQUID TREATING BATH CONTAINING AN AQUEOUS UNREACTED MIXTURE OF (1) ASUBSTANCE OF THE GROUP CONSISTING OF UREA AND GELATIN AND (2)FORMALDEHYDE, SAID COMPOSITION BEING KEPT AT A PH BETWEEN 2.2 AND 4.5WHEN SAID SUBSTANCE IS GELATIN AND BETWEEN ABOUT 4.0 AND 6.8 WHEN SAIDSUBSTANCE IS UREA, WHEREBY SAID SUBSTANCE AND FORMALDEHYDE REMAINUNREACTED IN THE PRESENCE OF WATER, FLOWING A STREAM OF STEAM PAST SAIDBATH AND CONSTRICTING THE FLOW OF STEAM TO CREATE A VENTURI EFFECTTHEREIN; WITHDRAWING MIXTURE FROM SAID BATH AND UNIFORMLY ENTRAININGSAME IN SAID STEAM FLOW BY MEANS OF SAID VENTURI EFFECT, THE AMOUNT OFCOMPOSITION WITHDRAWN FROM SAID BATH AND ENTRAINED IN SAID STEAM BEINGAUTOMATICALLY REGULATED BY THE AMOUNT OF STEAM PASSING THROUGH SAIDCONSTRICTED FLOW; DIRECTING A JET OF STEAM CONTAINING SAID MIXTUREAGAINST SAID SHEET WHILE SAID SHEET IS SUPPORTED BY SAID CORRUGATEDSURFACE, SAID STEAM BEING UNDER PRESSURE AND FLOWING AT A HIGH VELOCITYAGAINST THE SURFACE OF SAID SHEET, WHEREBY THE SHEET IS IMPREGNATED WITHA SUBSTANTIALLY UNIFORM ESSENTIALLY UNREACTED MIXTURE OF SAID SUBSTANCEAND FORMALDEHYDE, CONTINUOUSLY ADHERING SUBSTANTIALLY FLAT SHEETS TOOPPOSITE SIDES OF THE SHEET CONTACTED BY SAID STEAM, SUBSTANCE ANDFORMALDEHYDE, AND THEN HEATING SAID SHEET TO DRY SAME AND CONTINUINGSAID HEATING IN THE DRY CONDITION TO CAUSE A CONDENSATION REACTION OFSAID SUBSTANCE AND FORMALDEHYDE TO FORM A RESIN IN SITU UNIFORMLYDISPERSED IN SAID SHEET.